Access to various information movement and management (IM&M) resources, such as a telecommunications network, as well as to computer and banking facilities and information databases, is routinely obtained by users who can present evidence of permission to use the resource, in the form of a password, a Personal Identification Number (PIN), or another form of authorization code. The sophistication of access control systems has increased considerably and will continue to do so, as more and more features are added to the resources, and the value of the resources becomes greater. Entities that provide the resources want to have more control over the access process, want the security level to be high, and yet also want the access process to be "user friendly". However, "ease of use" generally translates to a certain lessening of security, and undesirably increases the possibility of unauthorized access as well as potential losses when security is breached. So far, by and large, the resource providers have absorbed the cost of "fraud" losses. Recently, some responsibility is being passed on to users such as large corporations that desire that their employees or customers have access to a resource. Unauthorized access presents a sizable problem that will only grow in the future. As losses due to hackers and other fraudulent users mount, and authorized users assume some liability for the losses, the demand for additional security will also grow.
The first step in preventing unauthorized access to resources and in protecting against fraud is to assign an authorization code, password or PIN to each authorized user, typically a code word of sufficient length so that a fraudulent user (also called a hacker) trying to break the code by multiple trial and error attempts using various possible combinations of the code will find it very difficult to gain access. This is because wrong combinations result in failed attempts and cause the access control system to "reset", so that the hacker has to "start again from the beginning." The time required to repeat the access process may be lengthy, and can even be intentionally increased to enhance security. See application Ser. No. 07/891,347 filed by McNair entitled "Access Control System" and assigned to the same assignee, now U.S. Pat. No. 5,375,244, issued Dec. 20, 1994.
The second step in access control and fraud prevention is to limit the number of failed attempts allowed for a particular user. (Note here and in the following discussion, that an "authorized user" may be an entity consisting of numerous individuals each of whom desirably can gain access to the resource. In this event, a single "authorized user" will have numerous authorization codes.) This is usually accomplished by a mechanism known as "lock-out", that maintains a record of the number of failed access attempts by a particular user and compares it with an established threshold. If the threshold is reached, the access control system blocks all subsequent access attempts originated by that user for a prespecified time, or until some action occurs to clear the record for that user. Typically, when each subsequent attempt is blocked, an announcement is made that the authorization code entered is invalid, even if a valid code is actually entered, so that trial and error guess work is not rewarded.
When a lock-out system is used, the appropriate degree of security against unauthorized access is obtained by having a sufficiently long authorization code and a sufficiently low threshold. A longer authorization code increases security, because the code is harder to guess, but forces the user to remember and accurately enter the longer code. A smaller threshold on the number of failed attempts also increases security because hackers are blocked more frequently, but comes with the possibility that a "valid" or authorized user may get locked out if the threshold is tripped due to inadvertent mistakes or simple memory lapses. In some cases, where failed attempts for several individuals (such as employees of the same company who are considered as a single user, or family members who share the same password, or individuals using telephone equipment with the same automatic number identification (ANI)) are accumulated, the threshold can be exceeded even before a particular individual attempts access. In most access systems that implement the lock-out feature, the record of failed attempts is refreshed periodically, typically after a certain time period without any failed attempts. A longer time period for refreshing increases security, but it also increases the risk of locking out authorized users, which can create bad publicity by giving the impression that the system is not providing good service.
Accordingly, it would be desirable to improve security in an access control system of the type that provides for lockout after a predetermined number of failed access attempts, while retaining a high degree of user friendliness.